The prosecution will have little difficulty proving that the defendant knew that the knapsack contained a bomb loaded with pellets and nails designed to kill and injure as many innocent children, including young children, as possible. Proponents of the death penalty will surely argue that if any case demands the ultimate penalty, this one does.

That is a strong argument, in light of the calculated nature of the intended mass killings. Nonetheless, I would hope that the Justice Department will decide against seeking the death penalty, even in light of the extreme depravity shown by the defendant in this case.

There are two fundamental reasons why the death penalty should not be imposed in this case. The first is the obverse of the argument that if anyone deserves the death penalty, it is this defendant. That may will be true. But it follows that if this defendant does not deserve the death penalty, then no one does.

In other words, a decision to withhold the death penalty in this case would be a powerful argument against the morality of the death penalty in any case. As a lifelong opponent of capital punishment in all cases, I would argue that not applying it in this case could have a considerable impact on the movement toward abolition.

This abolitionist argument is unlikely to have much impact on the Obama administration, which favors the death penalty, at least in extreme cases, such as this one. There is an argument, however, that could have an impact even on proponents of the death penalty.

Seeking the death penalty against Tsarnaev, and imposing it if he were to be convicted, would turn him into a martyr. His face would appear on recruiting posters for suicide bombers. The countdown toward his execution might well incite other acts of terrorism. Those seeking paradise through martyrdom would see him as a role model.

Whether the death penalty actually deters crime has been long debated. I have little doubt that some criminals may well be deterred by the prospect of execution rather than life imprisonment, though I am not certain how many. But I also have little doubt that some defendants, especially those motivated by ideological extremism, may be incentivized by the prospect of martyrdom.

There will be enormous political pressures on the Department of Justice to seek the death penalty in this case. Republican lawmakers would have a heyday attacking their Democratic opponents for being soft on terrorism if Attorney General Eric Holder decided not to seek the ultimate penalty. Whether or not Holder is influenced by this pressure, the pressure itself is a strong argument against capital punishment.

Life and death decisions should not be made based on political calculations. Several years ago, the US supreme court decided a case, in which a judge in a southern state was threatened with electoral defeat if he did not impose the death penalty after a jury had recommended against it. The supreme court upheld the judge's decision to impose the death penalty, over a strong dissent.

Fortunately, under American law, there is an additional check on the imposition of capital punishment. A jury must decide to impose the death penalty based on a balancing of aggravating and mitigating factors. If this case is tried in Massachusetts – a state that has abolished the death penalty – the jury pool may well contain some people who would be skeptical about executing a man like Tsarnaev. To be sure, the jury pool will be skewed by a rule that eliminates any potential juror who has a conscientious scruple against ever imposing the death penalty. But those who have an open mind about its applicability in any particular case may serve.

One of the hardest decisions Tsarnaev's defense lawyer has to make is whether to keep the case in Boston or whether to seek a change of venue to another location. The argument for moving the case out of Boston is obvious: virtually every Bostonian regards himself or herself as a victim of this horrendous crime, which brought the entire city to a standstill. But it may turn out that Boston jurors would be less likely to impose the death penalty in this case than jurors in other areas.

In the end, this case is more likely to be about whether Tsarnaev lives or dies than about whether he is guilty of this monstrous crime. If he planted the bomb, Tsarnaev chose death. We should respond by choosing life.